The proposed work involves investigation of the activities of a number of enzymes from metabolic pathways involved in pyrimidine and nucleic acid biosynthesis in developing rat cerebellum under conditions of hypo- and hyperthroidism, hyperglucocorticoidism, and undernutrition. Additionally, the studies will involve the interrelationships between corticosterone, rat growth hormone, and rat TSH, as well as several other hormones in serum of rat pups subjected to these perinatal endocrinopathies and undernutrition. Further investigations will involve the effects of these endocrine and nutritional perturbations on the onset of corticosterone circadian rhythms.